1. The specific activities of cytochrome c oxidase, catalase, succinate dehydrogenase, succinate–cytochrome c oxidoreductase, NADH–cytochrome c oxidoreductase, and NADPH–cytochrome c oxidoreductase in mid-exponential-phase batch cultures of glycerol-grown Schizosaccharomyces pombe indicated that the organisms were catabolite-de-repressed. 2. In cultures growing synchronously in the presence of glycerol as sole carbon source, the respiration rate showed two abrupt increases at about 0.45 and 0.95 of the cell-cycle and remained constant in the periods between successive rises. 3. Catalase, succinate dehydrogenase, NADH–cytochrome c oxidoreductase and acid p-nitrophenyl-phosphatase all showed peak patterns of expression in synchronous cultures. 4. Cytochrome c oxidase and cytochromes a+a3 both showed step patterns of expression with two rises per cell-cycle. 5. Cytochromes c548, b554 and b560 all followed similar time-courses in step patterns of expression, but these were distinct from, and more complex than, that of cytochromes a+a3. 6. These results are compared with those previously obtained with glucose-grown cultures, and the part played by catabolite repression in the expression of respiratory activities in the cell-cycle is assessed.

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